A Coupled Mathematical Model to Predict the Influence of Nitrogen Fertilization on Crop, Soil and Groundwater Quality

Intensified use of nitrogen based fertilizers in agriculture has resulted in a significant increases in soils and groundwater nitrate concentrations all over the world. Here we propose a new coupled model which describes the physical transport and biogeochemical dynamics of the water and nitrogen compounds in a soil-water-plant-groundwater system. Our model takes into account water infiltration into an unsaturated porous medium, the complex biogeochemical cycle of nitrogen in soils, nitrate leaching from the agricultural system toward the aquifer's water table, and the dispersion of nitrates in the groundwater. We calibrate our model and analyse the influence of soil type, precipitation or irrigation regime and fertilization schedules on leaching to groundwater as well as the temporal and spatial evolution of the nitrate pollutant plume in the aquifer. Simulations indicate that in order to achieve high crop yields while minimizing nitrogen loading to soils and groundwater we need to create an optimal balance between the amount of chemical fertilizers and water applied to crops on one hand, and the amount of nitrate and water used by plants on the other. We find that medium soils are more suitable for a sustainable corn production than coarse soils, ensuring both higher yield and less nitrate pollution of the aquifer. Regardless of soil type and irrigation schedule, a gradual fertilization throughout the plant life cycle reduces the potential for leaching and aquifer pollution. For medium soils, a more modest irrigation schedule results in more nitrate available for crops and less net leaching to the groundwater